Since electronic device generates heat during operating, it will damage easily due to overheat without effective heat-dissipation. It is common to install a DC fan without bushing on electronic device for hest-dissipating. The DC fan without bushing has been well known to equip various bearings like a ball bearing or an oily bearing between fan and fan housing in order to enhance rotation and diminish noise for fan. The oily bearing possesses porous structure made by sintering copper alloy or iron alloy so as to absorb lubricant. However, the lubricant will be pushed to sputter by rotating a fan shaft to contaminate entire fan housing when the fan shaft in the oily bearing rapidly rotates, and the oil-retaining quantity of oily bearing reduces and distributes unevenly. Therefore, when the fan is used for a long time, the lubricating efficiency of bearing becomes bad gradually and noise of bearing becomes loud gradually, even the fan will stop rotating.
A heat-dissipating fan was disclosed in R.O.C. Taiwan Patent No. 471557 entitled “lubricating oil-circulating structure for fan shaft”, which is composed of a housing, a stator and a rotor. A bearing has a bearing body with through holes and a ring portion is extended from one end of the bearing body to form an oil tank. A trench is set on the bearing body to make the released lubricant flow to the trench by passing the through holes then return to the oil tank and the through holes by passing the trench. Since the oil tank is set at the ring portion of the bearing and the trench is set on the bearing body, the lubricant will flow to the ring portion of the bearing and easy to contaminate the housing and oil-retaining quantity of bearing will decrease to weaken lubricating effect. Besides, the oil tank and the trench are the shape of a line easy to result in gathering lubricant at one side only, so that the oil-circulating efficiency of lubricant becomes worse.